Microscopy resources, techniques, and materials for classroom observations:

This is a compound microscope equipped with an adjustable substage condenser lens and an illumination field-limiting aperture (just above the light source).

Microscopes

One or more compound microscopes, preferably binocular, with 10 X ocular lenses, and 6, 10, and 40 X objective lenses will be needed. These will give a total magnification of 60, 100, and 400X, respectively. Students can be asked to figure out magnification by multiplying the magnification factors for ocular and objective lenses. Microscopes that have adjustable field limiting apertures and condensers are best, because these can be aligned for optical image viewing. Taking pictures of plankton is enjoyable, so it is nice to also have a photographic system, especially a digital camera, video camera, or digital video camera attached to a microscope.

Aligning a compound microscope

Better images will be observed if the microscope is aligned and illumination field adjusted for each magnification. To accomplish this, place a prepared elide of a thin object, such as diatoms or sectioned plant or animal tissue on the microscope stage and focus the image at the desired magnification. Then close the illumination field limiting aperture at the bottom of the microscope until you can see its edges through the lenses.

This image of the field limiting aperture needs to be focused, by moving the condenser height, and it needs to be centered by moving the image laterally.

Now move the condenser knob until the edges of the aperture are sharp; you may see a change from red to blue flare at the edges. Set the condenser at this sharp, flare point. Now move the two knobs that align the condenser until the image of the field limiting aperture is centered

This field limiting aperture is correctly positioned.

Finally, open the field limiting aperture until the edges are just out of view. This setting should be adjusted each time a different magnification is used.